1. Field of the Invention
The invention relates to a valve for the substantially gastight interruption of a flow path, according to the preamble to claim 1. Such valves, particularly in the form of shuttle valves or slide valves, are used, above all, in vacuum technology.
2. Description of the Background Art
A valve according to the preamble to claim 1 is known from US 2007/0138424 (Geiser), which is regarded as the closest prior art.
Valves of the type stated in the introduction are known in different embodiments from the prior art and are used, in particular, in vacuum chamber systems in the field of IC, semiconductor or substrate production, which must take place in a protected atmosphere as far as possible without the presence of contaminating particles. Such vacuum chamber systems comprise, in particular, at least one evacuatable vacuum chamber, designed to receive semiconductor elements or substrates which are to be machined or produced, which vacuum chamber possesses at least one vacuum chamber opening, through which the semiconductor elements or other substrates can be led into and out of the vacuum chamber, and further comprise at least one vacuum pump for evacuating the vacuum chamber. For instance, in a production plant for semiconductor wafers or liquid-crystal substrates, the highly sensitive semiconductor or liquid-crystal elements pass sequentially through a plurality of process vacuum chambers, in which the parts located within the process vacuum chambers are machined by means of a respective machining device. Both during the machining process within the process vacuum chambers and during the transport from chamber to chamber, the highly sensitive semiconductor elements or substrates must always be in a protected atmosphere—in particular in an airless environment.
To this end, on the one hand peripheral valves for opening and closing a gas intake or gas discharge and, on the other hand, transfer valves for opening and closing the transfer openings of the vacuum chambers for the introduction and removal of the parts are used.
The vacuum valves which are passed through by semiconductor parts, due to the described field of application and the therewith associated dimensioning, are referred to as vacuum transfer valves, due to their rectangular apertural cross section, also as right-angle valves and, due to their normal working method, also as slide valves, right-angle slide valves or transfer slide valves.
Peripheral valves are used, in particular, to control or regulate the gas flow between a vacuum chamber and a vacuum pump or a further vacuum chamber. Peripheral valves are found, for instance, within a pipe system between a process vacuum chamber or a transfer chamber and a vacuum pump, the atmosphere or a further process vacuum chamber. The apertural cross section of such valves, also termed pump valves, is generally smaller than in a vacuum transfer valve. Since peripheral valves, depending on the field of application, are used not only to fully open and close an opening, but also to control or regulate a flow rate by continuous adjustment of the apertural cross section between a fully open setting and a gastight closed setting, they are also referred to as regulating valves. A possible peripheral valve for controlling or regulating the gas flow is the shuttle valve.
In a typical shuttle valve, as known, for instance, from U.S. Pat. No. 6,089,537 (Olmsted), in a first step a generally round valve disk is rotationally pivoted, via a generally likewise round opening, from a setting which frees the opening into an intermediate setting which covers the opening. In the case of a slide valve, as described, for instance, in U.S. Pat. No. 6,416,037 (Geiser) or U.S. Pat. No. 6,056,266 (Blecha), the valve disk, as, too, the opening, is normally of rectangular configuration and, in this first step, is slid linearly from a setting which frees the opening into an intermediate setting which covers the opening. In this intermediate setting, the valve disk of the shuttle or slide valve is in a remote opposition to the valve seat surrounding the opening. In a second step, the distance between the valve disk and the valve seat is reduced, so that the valve disk and the valve seat are pushed uniformly closer together and the opening is closed off in a substantially gastight manner. This second motion is preferably made substantially in a perpendicular direction to the valve seat. The sealing can be realized, for example, either via a seal ring which is disposed on the close-off side of the valve disk and is pressed onto the valve seat running around the opening, or via a seal ring on the valve seat, against which the close-off side of the valve disk is pushed. As a result of the two-step closing operation, the sealing ring between the valve disk and the valve seat is barely subjected to shearing forces which would destroy the sealing ring, since the motion of the valve disk in the second step takes place substantially in a straight line perpendicularly to the valve seat.
From the prior art, different drive systems for obtaining this combination of a, in the case of the shuttle valve, rotatory and, in the case of the slide valve, translatory motion of the valve disk parallelly over the opening, and a substantially translatory motion perpendicularly to the opening are known, for instance from U.S. Pat. No. 6,089,537 (Olmsted) for a shuttle valve and from U.S. Pat. No. 6,416,037 (Geiser) for a slide valve.
The pressing of the valve disk onto the valve seat must be realized such that both the required gas-tightness is ensured within the whole of the pressure range, and damage to the sealing medium, in particular of the sealing ring in the form of an O-ring, as a result of excessive pressure load is avoided. In order to ensure this, known valves provide a contact pressure regulation of the valve disk which is governed by the pressure difference prevailing between the two valve disk sides. Particularly in the case of large pressure fluctuations or the change from underpressure to overpressure, or vice versa, a uniform force distribution along the whole of the periphery of the sealing ring cannot, however, always be ensured. In general terms, it is endeavored to decouple the sealing ring from supporting forces deriving from the pressure present at the valve. In U.S. Pat. No. 6,629,682 (Duelli), a vacuum valve having a sealing medium is proposed to this end, which vacuum valve is composed of a sealing ring and an adjacent supporting ring, so that the sealing ring is substantially rid of supporting forces.
In order to achieve the required gas-tightness, where necessary both for overpressure and underpressure, additionally or alternatively to the second motional step, some known shuttle valves or slide valves provide a valve ring which is displaceable perpendicular to the valve disk and surrounds the opening and which, for the gastight closure of the valve, is pushed onto the valve disk. Such valves having valve rings which are actively displaceable relative to the valve disk are known, for instance, from DE 1 264 191 B1, DE 34 47 008 C2, U.S. Pat. No. 3,145,969 (von Zweck) and DE 77 31 993 U. In U.S. Pat. No. 5,577,707 (Brida) a shuttle valve comprising a valve housing, which has an opening, and comprising a valve disk, which can be pivoted parallelly over the opening, for controlling a flow rate through the opening, is described. A valve ring, which encloses the opening, is actively movable vertically in the direction of the valve disk by means of a plurality of springs and compressed air cylinders. A possible refinement of this shuttle valve is proposed in US 2005/0067603 A1 (Lucas et al.).
U.S. Pat. No. 6,561,483 (Nakagawa) and U.S. Pat. No. 6,561,484 (Nakagawa et al.) disclose vacuum valves in different embodiments which comprise a divided valve disk. A first disk portion, which bears an axial seal, possesses an opening. A second disk portion is connected to the first disk portion by means of an expandable body. An actuator is disposed between the first and the second disk portion, so that the two disk portions can actively be moved closer together and farther apart. The expandable body is configured as a bellows. The first disk portion can be pressed by means of the actuator against the valve seat, so that an axially sealing contact is obtained, wherein the second disk portion—particularly in the case of an overpressure present on the valve seat side—is supported, where necessary, on an opposite valve housing side. The structure of the described vacuum valves, especially due to the large number of component parts and the need to use a bellows to seal off the first disk portion from the second disk portion, as well as, in some cases, a separate drive within the bellows, is relatively complex. Moreover, the described valves are awkward to maintain and prone to dirt contamination. Furthermore, the axial seal is not fully rid of differential pressure forces present at the valve, so that the axial contact pressing force is subject to certain fluctuations, whereby the wear on the axial seal is increased or leaks can be formed, particularly if the contact pressure of the axial seal is too low.
A further disadvantage of such valves having an actively adjustable valve ring is the relatively complicated and installation space-intensive structure of the valve, the need for complex control of the contact pressing forces and the presence of a plurality of moving parts in the flow channel, which make maintenance and cleaning of the valve more difficult.
Especially due to the field of application of shuttle and slide valves between process chambers and vacuum pumps in long production plants, a flattest possible structure of the valve in relation to the distance from opening to opening is required, for instance in order to keep the transport paths of the parts or gases short and the inner gas total volume low, and to arrange the individual components of the production plant as close together as possible and thus allow a compact construction of the production plants. This requirement for numerous applications is only inadequately met by valves, in particular, which have an actively adjustable valve ring or valve disk portions.
From US 2007/0138424 (Geiser) and US 2007/0138425 (Geiser), a valve, in particular a shuttle or slide valve, for the substantially gastight interruption of a flow path is known. The valve comprises a valve housing having a first wall, which wall has a first opening and a first valve seat, a valve disk having a close-off side comprising a sealing ring, and at least one drive. By means of the drive, the valve disk is pivotable or displaceable from an open position substantially parallel to the first valve seat and the vertical distance between the valve disk and the first valve seat is reducible such that, by virtue of an axially sealing contact between the sealing ring and the first valve seat, the flow path in the closed position is interrupted in a substantially gastight manner. The valve disk comprises an outer disk portion, on the rear side of which is disposed a star-shaped strut arrangement, which connects the outer disk portion to an arm, connected to a drive, in a central region situated close to the center axis of the first opening. The valve disk fixes the sealing ring perpendicular to the first valve seat. The valve disk further possesses an inner disk portion having an outer peripheral surface. The inner disk portion is mounted movably relative to the outer disk portion in a direction substantially perpendicular to the first valve seat. The outer peripheral surface is enclosed by the sealing ring such that a substantially gastight internal seal is formed. The sealing ring thus fulfills two sealing functions. On the one hand, it seals in the radial direction the joint between the inner and the outer disk portion, on the other hand, in the closed position of the valve, it seals in the axial direction the outer disk portion with respect to the valve seat. In the closed position, a pressure differential at the valve disk hence acts substantially upon the inner disk portion, so that the inner disk portion is supported, vertically decoupled from the outer disk portion, on a portion of the valve housing, in particular the first valve seat or a lateral groove. One advantage of this valve consists in the use of just a single seal, which has a dual function as an axial and radial seal. A disadvantage consists in the relatively complex structure of the valve and the need for a specific axial contact pressing force of the seal upon the valve seat to ensure the axial seal, for which reason the outer disk portion, by means of the rear strut arrangement connected centrally to the arm in order to avoid tilting, must be built relatively robust.